Java // 구현 // Client SocketChannel (in Server) // NIO NonBlocking

- NIO NonBlocking 기반 서버의 클라이언트 추상클래스

- NonBlocking이라서 receive() 메소드에 스레드를 할당하지 않아도 Selector가 메소드를 실행

- "route()"와 "terminate()"를  메소드 오버라이딩해서 처리

public abstract class Client {

    /*  Field */
    public SocketChannel socketChannel;
    public SelectionKey selectionKey;
    public Selector selector;
    public String response;
    private Charset charset = Charset.forName("UTF-8");

    /* Constructor */
    public Client(SocketChannel socketChannel, Selector selector) {
        try {
            this.socketChannel = socketChannel;
            this.selector = selector;
            this.response = "";

            // == OP_READ - SelectionKey 추가 ==
            this.socketChannel.configureBlocking(false);
            this.selectionKey = this.socketChannel.register(this.selector, SelectionKey.OP_READ);
            this.selectionKey.attach(this);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /* Receive */
    public void receive() {
        try {
            ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

            // == Request ==
            int byteCount = socketChannel.read(byteBuffer);
            if (byteCount == -1) throw new IOException(); // == close() 호출 (정상종료) ==
            byteBuffer.flip();
            String reqeust = charset.decode(byteBuffer).toString();

            // == route ==
            route(reqeust);

        } catch (IOException errB) {
            terminate();
        }
    }

    /* Route */
    protected abstract void route(String request);

    /* Send */
    public void send() {
        try {
            // == write ==
            selectionKey.interestOps(SelectionKey.OP_WRITE);
            ByteBuffer byteBuffer = charset.encode(this.response);
            socketChannel.write(byteBuffer);

            // == wakeup ==
            selectionKey.interestOps(SelectionKey.OP_READ);
            this.selector.wakeup();

        } catch (IOException e) {
            terminate();
        }
    }

    /* Terminate */
    protected abstract void terminate();

}